libperf: Add perf_record_header_attr_id()

The HEADER_ATTR record has an event attr followed by the id array.  But
perf data from a different version could have different size of attr.

So it cannot just use event->attr.id to access the array.  Let's add the
perf_record_header_attr_id() macro to calculate the start of the array.

Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Ian Rogers <irogers@google.com>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://lore.kernel.org/r/20230825152552.112913-2-namhyung@kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>

tools/lib/perf/include/perf/event.h

@@ -151,6 +151,10 @@ struct perf_record_header_attr {
 	__u64			 id[];
 };
 
+/* Returns the pointer to id array based on the actual attr size. */
+#define perf_record_header_attr_id(evt)			\
+	((void *)&(evt)->attr.attr + (evt)->attr.attr.size)
+
 enum {
 	PERF_CPU_MAP__CPUS = 0,
 	PERF_CPU_MAP__MASK = 1,